1. Field of the Invention
The present invention relates to fasteners, and more particularly to fasteners that enable a bolt to be secured through a blind hole, i.e., a hole in a panel wherein access may be had to only one side of the panel.
2. Description of Related Art
When fastening a bolt through a blind hole, one is confronted with the problem of providing a device on the blind side of the hole for retaining the bolt within the hole. One approach has been to insert a sleeve between the bolt and the side wall of the hole in order to frictionally engage the bolt within the hole. Examples of such sleeves are shown in U.S. Pat. No. 1,468,074, issued to R. S. Peirce and U.S. Pat. No. 3,373,647 issued to D. M. Sherock. A problem with such sleeves is that they depend on the strength and cohesiveness of the side wall of the hole for structural stability. In cases where the panel through which the hole extends is made from a friable or weak material, the sleeve may not provide adequate support for the bolt.
A more sophisticated sleeve is disclosed in U.S. Pat. No. 2,649,830, issued to J. W. Arnold. The Arnold sleeve includes a first portion for engaging with the side wall of the hole and a second portion for engaging with a threaded portion of the bolt. However, the Arnold sleeve is also dependent upon the structural integrity of the side walls of the hole, and further requires preparation of the surface adjacent the hole prior to its use. For example, recesses are required in the surface adjacent the hole to retain tabs projecting radially from the first portion of the sleeve.
A further problem with the sleeve-type devices is that they are not usable with thin panels, such as panels of sheet metal. In such cases, the side wall of the hole is very shallow, thus not providing a sufficient surface area for the sleeve to engage.
Others have attempted to retain a bolt in a blind hole by providing some kind of washer or nut that is able to be deformed or manipulated so as to be inserted through the hole, after which it can then be rearranged or reconfigured in a manner so as to engage the blind side of the panel through which the hole extends.
A commonly known example is the toggle bolt, which includes a collapsible crosspiece having a threaded portion in the center thereof through which a bolt is inserted. In operation, the crosspiece is collapsed at its center such that each half thereof lies parallel with the bolt, and is inserted through a hole. After insertion through the hole, the crosspiece, which is spring biased in an open position, unfolds so that it may function as a nut on the blind side of the surface containing the hole.
A problem with toggle bolts is that they are relatively complex in that they require a plurality of moving components that require assembly. An additional problem with toggle bolts is that they provide limited bearing contact with the blind side of the panel adjacent the hole and thus provide only limited absorption of stresses in a direction perpendicular to the longitudinal axis of the bolt. A further problem with toggle bolts is that they require a hole that is significantly larger than the diameter of the bolt used with the toggle.
U.S. Pat. No. 1,370,319, issued to J. Kennedy, discloses a form of toggle bolt that has a plurality of collapsible plate springs mounted at one end of a bolt and a standard nut at the other end of the bolt. In operation, the springs are collapsed and inserted through a blind hole in a panel until the springs are able to return to their normal, extended position. The nut is then tightened up on the bolt until a compressive force is exerted on the panel through which the bolt extends. The Kennedy toggle bolt suffers from the same disadvantages as the conventional toggle bolt described above in that it requires a plurality of components to assemble, and it makes only limited bearing contact with the surface adjacent to the hole through which the bolt is inserted. A further problem with the Kennedy toggle bolt is that is not usable on a standard bolt. It requires a special threaded shaft adapted to receive the plate springs.
U.S. Pat. No. 4,086,840, issued to R. A. Kurlander, discloses a hollow wall fastener that comprises a conical member comprised of an elastomeric material adapted to be collapsed radially for insertion through an opening. After it is completely inserted, it returns to its original configuration. The fastener is then deformed in a longitudinal direction in order to function as a washer on the blind side of the opening. A problem with the Kurlander fastener is that because it is made of an elastomeric material, the fastener is not able to withstand strong forces in the longitudinal direction.
U.S. Pat. No. 2,563,976, issued to E. Torosian, discloses a coiled attachment device that is intended for securing a bolt within a blind hole in a sheet metal panel. The Torosian device includes a spring washer of a specific gauge and pitch, and a coiled spring of a second gauge and pitch adapted to be collapsed within the center of the spring washer. The Torosian attachment device requires the careful alignment of the coiled spring within the center opening of the spring washer, and thus appears awkward to assemble and use. A further disadvantage of the Torosian attachment device is that it is only usable on thin panels that are able to fit between the gap in the spring washer.